Multiple potentiometer assembly



June 6, 1967 J. s. WAPNER MULTIPLE POTENTIOMETBR ASSEMBLY 3 Sheets-Sheet1 Original Filed June 25, 1958 INVENTOR.

3gOSEPH S. WAPNER ATTORNEY.

June 6, 1967 I J. s. WAPNER 3,324,438

I MULTIPLE POTENTIOMETER ASSEMBLY Original Filed June 25, 1958 3Sheets-Sheet 2 INVENTOR. g psepH s. WAPNER ATTORNEY-i June 6, 1967 J. s.WAPNER MULTIPLE POTENTIOMETER ASSEMBLY 3 Sheets-Sheet 3 Original FiledJune 25, 1958 JOSEPH S. WAPNER, BY

ATTORNEY;

United States Patent 3,324,438 MULTIPLE POTENTIOMETER ASSEMBLY Joseph S.Wapner, Levittown, Pa., assignor, by mesne assignments, to AmericanMeter Company, Incorporated, Philadelphia, Pa, a corporation of DelawareOriginal application June 25, 1958, Ser. No. 744,373, now

Patent No. 3,069,669, dated Dec. 18, 1962. Divided and this applicationMar. 28, 1962, Ser. No. 189,946

Claims. (Cl. 338-129) This application is a division of Ser. No.744,373, file-d June 25, 1958, now Patent 3,069,669. This application isdirected to the potentiometer assembly or array of the parentapplication. In a preferred form adapted for meters, but of more generalapplicability, the array is of like potentiometers, each having aresistance element and an associated wiper with the resistance elementsmounted on a base or plate and the wiper elements respectively mountedon a different meter register shaft so the position of each wipercorresponds to a different digit of the meter register. The accuracy ofthe potentiometers is improved by high conductivity conductors betweenthe input and output conductors of each potentiometer which are bridgedby a resistance coating. The input, output and high conductivityconductors of the potentiometers are connected in parallel so theaccuracy is less affected by variations in the resistivity of theresistance elements of the individual potentiometers. The resistancecoating may be removable to adjust its back and forth calibrationresistance. The potentiometer array is adapted to production by printedcircuit techniques.

The foregoing and other objects of the invention relating to variousdetails will become apparent from the following description, read inconjunction with the accompanying drawings, in which:

FIGURE 1 is a perspective view showing, in particular, the dialmechanism of a gas meter and the electrical elements associatedtherewith in accordance with the invention;

FIGURE 2 is a perspective view illustrating the box which is carried bya meter reader in accordance with the invention;

FIGURE 3 is a wiring diagram showing the electrical circuitry involvedin accordance with the invention; and

FIGURE 4 is a fragmentary sectional view illustrating a furtherembodiment of the invention which involves isolation of all electricalcircuitry from the interior of a gas meter.

Referring to FIGURE 1, there is shown therein the upper portion of aconventional gas meter, there being indicated at 2 the usual dial platecarrying markings with which cooperate the various pointers driventhrough the usual gearing 4 from the shaft 6 which is driven by themeter output shaft. The pointer shafts indicated at 8, 10, 12 and 14correspond to readings of gas volume and may, for example, correspondrespectively to thousands, tens of thousands, hundreds of thousands andmillions of cubic feet. What is shown herein is consistent with theusual arrangement in which the successive shafts have oppositedirections of rotation for increasing readings. For example, the shaft 8in FIGURE 1 may rotate counterclockwise while the shaft 10 rotatesclockwise, and so on, for increasing readings. In accordance with apreferred form of the invention, the dials on the front of the meterpresent their usual aspects for direct readings, the novel parts of thearrangement being mounted behind the gearing and being particularlyassociated with a printed circuit board 16 mounted by posts 18, thepointer shafts being extended for the present purposes. As will beevident as the description proceeds, the dial assemblies of meters maybe replaced by the new assemblies illustrated in FIGURE 1, most of theparts of the old ones being 3,324,438 Patented June 6, 1967 then reusedin forming the new assemblies. As will become evident the changesinvolve primarily the addition of a printed circuit board andpotentiometer contacts mounted on the pointer shafts with the additionof a multiple conductor cable running to an external connector.

A potentiometer is associated with each of the shafts 8, 10, 12 and 14as follows:

Each potentiometer comprises an interrupted circular resistance 20surrounding an opening 19 in the printed circuit board 16. Theparticular nature of this resistance will be described hereafter. Itsend at the zero of measurement is indicated at 22 and its end at themeasurement of 10 is indicated at 24, these ends being only slightlyspaced from each other. The wiring diagram shows these resistances inconventionalized fashion as involving in each case five sections joinedin series. The ends 22 of all of the resistances are connected to aterminal 26 While the ends 24 are all connected to a terminal 28.

On each of the shafts 8, 10, 12 and 14 there is mounted an insulatinghub 30 fixed against rotation and mounting at the rear of the printedcircuit board 16 a conducting wiper arm 32 provided with a contactportion 34 having limited circumferential engagement with theresistance. The hub 30 is also provided with a second arm 36 which hasan extension continuously making contact with an annular ring of goodconducting material which is printed on the board 16 on its front face,this ring not being indicated in the figures. These various rings of theseveral potentiometers are connected to the terminals 38, 40, 42 and 44as indicated in FIGURE 3.

If the potentiometers consisted solely of printed resistance materialengageable by the contact arms 32, there would be very considerableerror involved in correspondence of output potentials with angularpositions of the wiper shafts unless the printing of the resistance wasvery carefully accomplished, which latter would be a matter of greatexpense. One of the objects of the present invention is the provision ofa printed potentiometer arrangement which has a high degree of linearrelationship of output potential to angular position of a wiper contactdespite the fact that the printing involved is very inexpensive andaccomplished without the exercise of any substantial care in the way ofsecuring uniformity. For this purpose, before the resistance material at20 is applied, the good conducting elements of the printed circuit areformed by any one of the usual conventional processes on the board.These conducting elements comprise, as indicated for the left handpotentiometer in FIG- URE 1, radial portions 46, 48, 50, 52, 54 and 56over which the resistance material is provided by painting, printing, orother procedures. These conducting elements are so arranged as to dividethe resistance ring in a number of equal segments which are illustratedas five in number, though as will be obvious, other segments may equallywell be provided. Because of the high conductivity of the elements 46 to56, the various segments are bounded at their ends by equipotentiallines, so that the complete resistance 20 in the case of eachpotentiometer is effectively broken up into separate independentresistances such as are electrically diagrammed in FIGURE 3. ConsideringFIGURE 3 and so much of the printed circuitry as appears at the rear ofthe board 16 (the additional, and obvious, remaining printed circuitryat the front of the board not being shown) the corresponding elements ofthe groups 46 to 56 of the various potentiometers are interconnected sothat the segments which they delimit are arranged electrically inparallel as illustrated in FIGURE 3.

Additionally, the various conductors connected to the equipotentialelements of the potentiometers are electrically extended as indicated at58, 60, 62, 64, 66 and 68 so as to underlie and provide equipotentiallines across a rectangular resistance area 70 applied over them in thesame fashion as the resistance areas 20 of the potentiometers.Additional segments are thus provided in parallel with the potentiometersegments to give rise to the electrical array shown at the left ofFIGURE 3. The segments of the resistance area 70 are provided forcalibration adjustments which may be made very simply. Considering, aswill become clearer hereafter, current input from terminals 26 and 28across the parallel potentiometers and the parallel resistance area 70,what is desired is that the resistances offered across the successiveparallel groups of segments should be equal. In other words, the totalresistance appearing between 46 and 48 should be equal to that between48 and 50, between 50 and 52, and so on. Assuming for example, that thevoltage drop between terminals 26 and 28 is 50 millivolts (a typicalvalue which may be provided for in operation) and assuming 28 to have areference zero potential, it is desirable that the potential of theeffective conductor 48 should be millivolts, that of conductor 50, 20millivolts etc. This result can be achieved by equalizing the resistancegroups and this is most readily accomplished in calibration merely byscratching or cutting notches such as indicated at 72 in FIGURE 1 intothe resistance segments, the resistances of these segments beingoriginally made too low. These notches may be made in succession withsuitable connections to the equipotential conductors involved. If, bychance, too much material is removed, the error may be readily remediedmerely by adding some additional resistance material by means of abrush, stamp pad, or the like, this added resistance material becomingparallel to that already present and thus lowering the resistance. Theboard is completed for assembly when the various resistances areequalized.

The purpose and effect of the foregoing will now be apparent. While itwould be very difficult using an inexpensive method of applyingresistance material to secure uniformity throughout the approximate 360of each potentiometer resistance, the resistance between two suchequipotentials as 48 and S0, for example, may depart to a veryconsiderable degree from uniformity or linearity without making anymaterial difference to the ultimate reading. For example, the positionof the equipotential conductor 48 of the left hand potentiometer inFIGURE 1 would correspond to the digit 2 in the measurement of thousandsof cubic feet while the potential at 50 would correspond to 4. As willhereafter appear these potentials are actually read on meters, and ifthe meters are calibrated in digits, there can be no substantialconfusion in proper interpolationbetween the readings of 2, 3 and 4occasioned by the presence of the contact 34 in the resistance segmentin question. Clearly, with somewhat more elaboration, ten segments couldbe provided in each potentiometer resistance, but this is quiteunnecessary for the purposes here involved. In fact, it is quitesatisfactory to provide only four segments instead of five.

As indicated in FIGURE 3, the several terminals 26, 28, 38, 40, 42 and44 are connected to a meter terminal board 74, to terminals of which areconnected the conductors of a cable 75 the conductors being in turnconnected to pins or sockets of a connector element 78 which may besecured to the exterior of the wall of a building in which the meter iscontained. The other element 80 of the connector provided at 76 has itsterminals connected through a cable 82 (see also FIGURE 2) which isconnected into a box 84 to be carried by the meter reader.

The right hand portion of FIGURE 3 shows the electrical elements locatedwithin the box 84. The physical arrangement is immaterial, and hence theelectrical diagram alone is illustrated. To keep this box compact, itinvolves, desirably, transistor amplifiers and semiconductor rectifiersassociated with other miniature elements including small size meters. Abattery 86 supplies D.C. power and to provide automatic switching, alead 88 extends to one of the terminals of connector element while alead 92 extends from another terminal, shorting between these terminalsbeing provided by a connection in the associated connector element 78.Thus except when the box assembly is plugged in, the battery circuit isopened.

The battery supplies power to an oscillator 94 which is desirably of aminiature transistor type and may take any conventional form. An audiofrequency is desirably generated and a frequency of five hundred cycleshas been found convenient though the frequency is subject to widechoice. The oscillator output is delivered through a proper matchingtransformer 96 to the conductors 98 and 100 which lead to thesupplyterminals for the potentiometers at 26 and 28. In one of these leadsthere is provided the adjustable resistance 102 which may be set by themeter reader to secure a standard output potential between theconnectors '98 and 100 which may typically be about 50 millivolts. Toenable the reader to ascertain that this adjustment has been properlymade, connection 104 is made through the two stage transistor amplifierarrangement 106 the output of which is delivered to the bridge rectifier108 to operate the direct current zero set meter 110 which may beprovided with a single marking to which the pointer is adjusted bymanipulation of the knob 102 which adjusts resistance 102. Through theplugin connections which may be followed in FIGURE 3, the successiveterminals 38, 40, 42 and 44 are connected respectively to the leads 114,116, 118 and 120 providing inputs to the two stage transistor amplifiers122, 124, 126 and 128 which respectively supply the diode bridges 130,132, 134 and 136 energizing the meters 138, 140,

142 and 144 which respectively read in terms of the digitscorrespondingto thousands, tens of thousands, hundreds of thousands and millions ofcubic feet. The operation will now be evident and is, briefly, asfollows:

When a reading is to be made, the meter reader carrying a box 84, plugsthe connector 80 into the mating connector 78 in the building wall,adjusts the knob 102' to secure a zero setting on the meter 110, andthen reads from the meters 138, 140, 142 and 1 44 the same values whichhe would normally read from the dials on the faceof the meter. Thisreading can be accurately accomplished due to the characteristics of thepotentiometers and the precalibration thereof as previously described.As in the case of direct reading of the pointers with respect tothedials on the face of the meter, comparison of the successive pairs ofthe D.C. meters will leave no question of the values to be read. Forexample, if a pointer of one of the milliamineters reads between the 3and 4, and the preceding meter reads, for example, 7, it will be obviousthat the reading of the first should be 3 rather than 4. Even greatnon-uniformity of the potentiometer resistances will not give rise toindefinite reading in this respect.

In some cases it may be required that no electrical circuitry be exposedto the interior of a gas meter housing, and it may be desirable toaccomplish the ends of the present invention without any substantialmodification of the standard meter mechanism. In such cases, thearrangement illustrated in FIGURE 4 may be adopted. The meter is hereindicated at and comprises the usual dial plate 2' carrying markingswith which cooperate the various pointers driven through theconventional gearing 4 from the shaft 6 which is driven by the meteroutput shaft. A box 152 provides an enclosure for the readout means andmay be formed of brass or other material Welded or soldered into anopening provided in the gas meter casing. Within this box 152 there islocated a gear mechanism 154 which may be essentially a duplicate of thedial mechanism with the exception that the dial plate and pointers maybe omitted. The gearing 156 is driven by the shaft 158, corresponding toshaft 6.:

of FIGURE 1, and serves to drive the contact wipers 160 and 162associated with a printed circuit arrangement which may be the same asthat described with reference to FIGURE 1. To provide a drive whichinvolves no passage of a shaft from the interior of the meter into thebox 152, the shafts 6' and .158 are provided with meshing magnetic gears164 and 166 which come into close proximity on opposite sides of thebrass wall 170 of the box. These gears are in the form of ceramicmagnets provided with a plurality of alternating north and south poleson their cylindrical surfaces so that as the gear 164 rotates it willdrive the corresponding gear 166. Other types of magnetic couplings may,of course, be provided, operating through a wall which provides thedesire-d isolation.

What is claimed is:

1. An array of like potentiometers each of which comprises a base, inputand output conductors carried by said base, a plurality of otherconductors of high conductivity carried by said base between said inputand output conductors and spaced from each other and from said input andoutput conductors whereby each potentiometer in the array hascorresponding input, output and other conductors in like relation, acoating of resistance material bridging said input, output and otherconductors, and a contact element movable in contact with said coatingbetween said input and output conductors and across said otherconductors, and means electrically connecting in parallel correspondinginput, output and other conductors of said potentiometers.

2. An array of like potentiometers each of which comprises a base, acontact element mounted for rotation relative to said base about anaxis, input and output conductors carried by said base, a plurality ofother radially disposed conductors of high conductivity carried by saidbase between said input and output conductors and spaced from each otherand from said input and output conductors whereby each potentiometer inthe array has cor-responding input, output and other conductors in likerelation, and a coating of resistance material dis- I posedconcentrically with said axis and bridging said tentiometers of thearray, a plurality of further other con- 5 ductors of high conductivitycarried by said base between the last mentioned further input and outputconductors and spaced from each other and from said further input andoutput conductors on a spacing corresponding to the spacing of saidother conductors of the potentiometers, and a coating of removableresistance material bridging the last mentioned further input, outputand other conductors, and means electrically connecting in parallel thelast mentioned further input, output and other conductors tocorresponding input, output and other conductors of the potentiometers.

4. An array of potentiometers according to claim 2 comprising furtherinput and output conductors corresponding to the input and outputconductors of the potentiometers of the array, a plurality of furtherother conductors of high conductivity carried by said base between thelast mentioned further input and output conductors and spaced from eachother and from said further input and output conductors on a spacingcorresponding to the spacing of said other conductors of thepotentiometers, and a coating of removable resistance material bridgingthe last mentioned further input, output and other conductors, and meanselectrically connecting in parallel the last mentioned further input,output and other conductors to corresponding input, output and otherconductors of the potentiometers.

5. A potentiometer assembly comprising a unitary insulating bearingplate, a plurality of spaced generally circular resistance elements onone surface of the plate, shafts extending through the centers of theresistance elements and mounted in apertures in the plate, each shaftcarrying a wiper in rotatable contact with the resistance element, sliprings on the plate concentric with the resistance elements, each wiperhaving a slip ring contact in sliding contact with its respective slipring, terminals extending back through the plate connected to theelement ends and to the slip rings, and a gear train interconnecting allof the shafts.

References Cited UNITED STATES PATENTS 2,134,870 11/1938 Fruth 338-162 X2,269,136 1/1942 Tellkamp 338312 X 2,280,775 4/1942 Mirk 338-129 X2,744,986 5/1956 Caldwell 338l42 X 2,799,756 7/1957 Graham 338-1212,866,052 12/1958 Bourns 338129 0 ANTHONY BARTIS, Primary Examiner.

RICHARD M. WOOD, Examiner.

1. AN ARRAY OF LIKE POTENTIOMETERS EACH OF WHICH COMPRISES A BASE, INPUTAND OUTPUT CONDUCTORS CARRIED BY SAID BASE, A PLURALITY OF OTHERCONDUCTORS OF HIGH CONDUCTIVITY CARRIED BY SAID BASE BETWEEN SAID INPUTAND OUTPUT CONDUCTORS AND SPACED FROM EACH OTHER AND FROM SAID INPUT ANDOUTPUT CONDUCTORS WHEREBY EACH POTENTIOMETER IN THE ARRAY HASCORRESPONDING INPUT, OUTPUT AND OTHER CONDUCTORS IN LIKE RELATION, ACOATING OF RESISTANCE MATERIAL BRIDGING SAID INPUT, OUTPUT AND OTHERCONDUCTORS, AND A CONTACT ELEMENT MOVABLE IN CONTACT WITH SAID COATINGBETWEEN SAID INPUT AND OUTPUT CONDUCTORS AND ACROSS SAID OTHERCONDUCTORS, AND MEANS ELECTRICALLY CONNECTING IN PARALLEL CORRESPONDINGINPUT, OUTPUT AND OTHER CONDUCTORS OF SAID POTENTIOMETERS.